Preparation of lewisite



Patented Mar. 29, 1949 PREPARATION OF LEWISITE Paul D. Bartlett, Weston,and Hyp Joseph Dauben, Jr., Cambridge, Mass, and Leonard J.

Rosen, Cumberland, Md.

No Drawing. Application May 22, 1944, Serial No. 536,848

6 Claims. 1

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment to us ofany royalty thereon.

This invention relates to a method of improving catalytic synthesestypified by a union of an organic compound, such as an unsaturatedhydrocarbon, with a polar or inorganic compound.

It is particularly concerned with increasing the efiiciency of catalystshaving moderate or low activity in the syntheses reactions for obtaininghigher yield rates of desired specific products with ease of operatingcontrol.

Narrowly considered for the purpose of elucidation, an object of thisinvention is to provide a suitable agent for promoting the catalyticactivity of a mercuric chloride catalyst in the addition reaction of anunsaturated aliphatic hydrocarbon, acetylene, with the polar inorganiccompound, arsenic trichloride, to substantially increase the yield andoutput rate of chlorovinyldichloroarsine a war gas known as lewisite.

As in various other syntheses, the early method of preparing lewisiteinvolved the use of anhydrous aluminum chloride as a catalyst. Thiscatalyst has an intense activity which makes the reactions complicatedand at times dangerous. With the excessively vigorous catalyst, manyundesired side reactions occur, such as fission and polymerization,resulting in a degradation of the product. In the production of lewisitewith anhydrous aluminum chloride, considerable heat is evolved andviolent explosions may occur. The reaction leads to the formation inlarge quantities of undesired secondary and tertiary products, tar, andsome materials which are also explosive.

Accordingly, efforts have been made to find catalysts less active thananhydrous aluminum chloride, as, for example, halides of other metals aswell as the double salt, sodium-aluminum chloride. These catalysts withmoderate or low activity, on the other hand, give too low a rate ofreaction in a number of reactions, especially at temperatures which aresufliciently moderate for proper control and avoidance of undesired sidereactions.

Prior to the discoveries leading to this invention, it was generallysuspected that various metal salts present as impurities in thereactants might have a detrimental or inhibiting effect on the ac tivityof a moderate catalyst. For example, arsenic trichloride was found tocontain chlorides of iron, silicon, aluminum, antimony, mercury,bismuth, tin, etc. in small amounts. On investigating the effects ofthese impurities in the lewisite reaction, surprisingly a, number ofthese same compounds proved to be promoters of catalytic activity whenpresent in adequate amounts.

In the example of the lewisite reaction, acetylene gas passed into astirred and heated mixture an unpromoited control run.

of arsenic trichloride and a solution of mercuric chloride inhydrochloric acid reacts with the arsenic trichloride to form a mixtureof betachlorovinyldichloroarsine, bis (beta-chlorovinyl) chloroarsine,and tris (beta-chlorovinyl) arsine. Vinyl chloride and small amounts ofacetaldehyde are formed as by-products.

The arsine derivatives differ by the successive addition to the arsenicrtrichloride of 1, 2, or 3 molecules of acetylene. The reactions arerepresented as follows:

(3 H; AsOl =ClCH:OH.As

(Ohlorovinyldichloroarsine) (Primary lewisite) OlOH:CH

2 02112) AsCl3= A801 OlOHzOH (Dichlorovinylchloroarsine) (Secondarylewisite) ClOHzCH 3(G2Hz) AsCla=OlCH:CH-As ClOH:OH

(Trichlorovinylarsine) (Tertiary lewisite) The rate of fixation ofacetylene depends on the concentrations of the mercuric chloride andhydrogen chloride, the temperature, rate of inflow of acetylene, andrate of stirring. When these factors are made constant, the inclusion ofany of several metallic chlorides, as SbCls, SbC15, FeCls, ZnClz, SUCH,and CdClz, in the reaction mixture leads to increased rates of acetylenefixation with corresponding increases in the rate of formation of theproducts and by-products. With a catalytic solution of 60% HgCl28%HCl-32% H2O, approximately saturated with the separate metallicchlorides, rates of acetylene fixation at 50 C. were increased up tothreefold over that of The effectiveness of the promotion in increasingabsorption rate is directly proportional to the molar concentration ofthe promoters in the reaction mixture.

The metallic chloride promoters are not acetylene-fixation catalystswhen dissolved in hydrochloric acid and, accordingly, do not function assuch in the mixture, nor are they acetylenated. The promoters functionby abstracting chloride ions from combination with the mercuricchloride. Mercuric chloride in hydrochloric acid exists in the formsHg++, HgCl HgClz, HgClr, HgCl4= and the correspondng dimeric species.The species containing the lower ratios of C1 to Hg function as the moreeffective acetylene-fixation catalysts as was shown by the use ofdifferent amounts of 20% hydrochloric acid to dissolve the same amountof solutions containing the lower Cl/Hg being t as best catalysts. Inthe presence of the metallic cnloridc promoters. all being good chlorideion acceptors, the chloride ions are extracted from the in the primarylewisite reaction. The addition of such a salt as antimony, tin, zinc.or iron chloride is one way of reducing the chloride ion conc rationwithout reducing the acidity, since dissolved mercuric chloride speciesto establish a 5 all these salts form stable 001 1 ions With newequilibrium mixture having a great proportion of the members with lowerCl/Hg ratios. Sbch +cy?gsbcl,r The promoters are not consumed by thereaction and the chloride and hydrogen ion balance is not ZnChi-Cl *Znchsufficiently altered to lead to increased hydrolysis A Similar p; can beachieved by t ti l of the ars nic trich rid and ts acetylfinatedreplacement of the hydrochloric acid by sulfuric p s in the favorableCaSeS- Increases 0f acid in the catalytic solution, but the chloride ion10 in the amount of vinyl chloride fo concentration is of someimportance in governocc rs with h re s y y yze p ing the hydrolysis ofarsenic trichloride and of moters. 15 the primary lewisite produced inthe reaction, Extensive studies have been made of the e cts and thischloride ion concentration is more easily of the various promoters andtheir concentrations t n by t use f lt of th sbC1 t pe, p n the r e nresults f th e tio Which yields back chloride ion when the equilib- Itwas observed that with concentrations of ri is disturbed. about andhigher, based on e W t 0 Solutions containing systems of this sort t e ty the metal a d s k wn 0 n together with arsenic trichloride tend, onreuse, $011 as Chloride-acceptors made a r increase to assume ahydrochloric acid concentration in t e accelerating b pt O 0f t eilcharacteristic of the equilibria present. In the rated hydrocarbon bythe Catalyst solution. The systems under discussion, this acidconcentration following table lists observed absorption rates is lo erthan that initially present. and primary lewisite yield rates obtainedWhen Characteristics of the effective promoters are 60% HgCl28% HC132%H2O catalytic layers summarized as follows: The promoters are salts weresaturated or almost saturated with the or compounds of multivalentmetals, preferably metal Ch oride promoters at 25 C. and the abof metalswhich exist in more than one stage sorptions run at 45 0.: of oxidation.The promoters having the higher Met. Ohlor. Promoter None SbGh SbCltFeCls ZIlClz SnCli CdCl2 g. Promoter/100g. cat. soln 7.. None 65.4 32.030.9 15.6 20.4 8.0 Av. rate in l/hr./l00 g. HgClg 11.8 35.9 as 20.0 19.217.8 15.0 g. Primary lewisite/hr./100 g. HgCh" 68.0 205.3 102.4 95.097.0 91.2 92.3 g. Primary lewisite/hr./l. reactorspace. 245 739 369 342349 328 332 There are three possible ways in which the molar solubilityin the catalyst solution exhibit promoters might function: (1) thepromoters proportionally higher absorption promoting rates. mightthemselves be acetylenated; (2) they might They do not precipitate outthe catalyst more function as independent catalysts, supplementing thana small amount. They do not undergo hythe action of the mercuricchloride catalyst presdrolysis to more than a small extent. They conent;(3) they might serve as adjuncts, or tain a metal or positiveconstituent which is promoters, for the mercuric chloride catalyst. moreelectropositive than the positive metal or The first possibility isruled out by the observaconstituent of the catalyst and also moreelection that in the absence of arsenic trichloride, tropositive thanthe positive metal or positive the only product is chlorovinylmercuricchloride, constituent of the polar reactant. They do not and thepromoter remains alomst entirely in absorb, combine or react with theorganic rethe aqueo p se e con possib lity is actant as readily as thecatalyst. eliminated since no reaction occurs without the The foregoingconsiderations are in accord mercuric chloride catalyst present.Therefore, with the facts that antimony trichloride is a the chloridesof the other metals, such as antisuperior promoter, zinc, stannic, andcadmium ny hl ri act trictly s promoters for chlorides are favorableover antimony pentachlothe mercuric chloride catalyst. ride and ferricchloride in promoting a mercuric There is evidence to show that theratechloride catalyst in the lewisite reaction, while te minin tep in hpreparation of primary phosphorus trichloride gives negative results.lewisite is the union of acetylene with the mer- Desirable properties ofthe promoter system curic chloride to give chlorovinylmercuricchlobesides a low vinyl chloride loss are a high rate ride. and thatthis reaction is the faster, the of absorption accompanied by small lossof greater the fraction of mercuric chloride in forms promoter, ease ofseparation of the catalyst and other than HgCl4=. The equilibriapromoter from the product, and homogeneity of the catalytic solution atthe end of the run. Hg+++cl (Hgcl+ The absorption rate promotingeffectiveness HgCl++Cl- I-IgCl2 of a good promoter, such as antimonytrichloride, varies linearly with the concentration of the promoter evenup to about a saturation concentra- Hgcls tion in the catalyst solution.Concentrations of can all be shifted to the left by any method ntimonyrichloricie, xp ssed as rams of pr of lowering the chloride ionconcentration. Since moter p8 0 grams O ytic So u o emthe potency ofthese mercuric species as acetylp oyed, e and 6 ene-fixation agentsdecreases with increasing this concentration range there was no increasenumber of chlorines attached to the mercury, a in vinyl chlorideformation over that of an ungeneral shift of these equilibria to theleft is promoted controlled run, within experimental attended by anincreased catalytic effectiveness error. However, in obtaining optimumresults.

other factors should be balanced against the increased rate of reaction.An increased promoter concentration slightly increases the proportion ofless desirable secondary lewisite and tends to increase the loss ofpromoter. Also increasing the ratio of the polar compound to thepromotedoatalytic solution increases the loss of the promoter.Accordingly, it is desirable to keep the concentration of the promoterand of the polar reactant Within optimum limits. In the mercuricchloride catalyzed lewisite reaction, satisfactory results are obtainedby using about 1% of antimony trichloride in the catalytic solution andhaving a ratio of about 1 gram of antimony trichloride to 162 grams ofarsenic trichloride.

In the event higher absorption rates are desirable, consequently withhigher promoter concentrations, the promoter loss may be reduced bycertain expedients. For instance, it is possible to recover all or alarge part of the promoter from the product by using an extraction witha solvent, such as 18% to 20% hydrochloric acid. The hydrochloric acidsolvent has the advantage of reducing the sludge content, and continuedreuse of the wash solution furnishes a fairly pure recovered antimonytrichloride. As another eX- pedient, the arsenic trichloride may be usedwith an organic solvent, e. g., methylcyclohexane, which reduces thesolubility of the promoter in the arsenic trichlorid'e.

Other types of moderate catalysts besides mercuric chloride having theproperty of absorbing the unsaturated hydrocarbon, acetylene, and whichare subject advantageously to a promoting action are cuprous cyanide,cuprous chloride, and mercuric cyanide. These catalysts give about thesame rate of acetylene absorption as mercuric chloride in 18%hydrochloric acid at 25 C. when they are used respectively at 95, 95 and33 C. They likewise may be used in hydrochloric acid solutions or insolutions with other solvents as, for example, ethanolaminehydrochloride.

In using any of the catalysts, the proportions of the reactants, theproportions of the catalyst chosen, the kinds and proportions of thepromoter and solvents, and the temperature may be varied within widelimits but depending upon the nature of the materials used, the productdesired, and rate desired. For example, in test runs that consistentlydemonstrated the promoting effect of antimony trichloridc on mercuricchloride, the

amount of acetylene used was varied from 8,210

cc. to 37,096 00., the mercuric chloride concentration in thehydrochloric acid solution was varied from 30 to 60%, the antimonytrichloride was varied from about 2% to 52% by weight of the solution,the amount of arsenic trichloride was varied from about 108 g. to 323g., and the temperature was varied from 24 C. to 45 C.

To summarize the characteristics of the catalysts: they are polarsubstances capable of readily absorbing the unsaturated hydrocarbonreactant and preferably contain a multivalent metal or positiveconstituent which is more elec tronegative than the metal or positiveconstituent of the polar reactant.

The specific results obtained have indicated that the efficiency of anycatalyst which functions by virtue of its electron-accepting ability maybe increased by the addition of a promoting substance, which possessesthe same kind of electron-accepting property, preferably to a higherdegree. The promoter may or may not operate as a catalyst for theoriginal reaction, but its principal function is to absorb negative ionsor groupings from the catalyst and thereby cause the latter to become amore effective catalyst.

Reactions such as addition, condensation, substitution, andrearrangement, in which the catalyst exhibits its action as the resultof a transient coordination with a negative or electron-donating group,are subject to this type of promoter action. The promoters may functionin either homogeneous or heterogeneous catalysis and either in liquid orvapor phase reactions.

Catalysts susceptible to the type of promoter action herein describedinclude organic and inorganic derivatives (such as halides, cyanides,sulfates, phosphates, hydroxides, nitrates, acetates and oxides) ofmetals or metalloids (such as Al, B, Fe, Hg, Cd, Cu, Ag, Sb, Sn, Zn),but are not limited by these examples. The promoters are compounds ofthe same type but preferably bear a certain relationship to the catalystunder the reaction conditions, as previously explained, for instance,being less reactive with the unsaturated hydrocarbon or organic reactantand containing a more electropositive metal or positive constituent.

More specifically, promoters may be used in.

the following reactions which are catalyzed by mercury compounds: (at)addition of hydrogen halides and organic acids to acetylene in formingvinyl halides and vinyl esters; (b) addition of water (hydration) toacetylene in forming acetaldehyde.

For example, using the same conditions as those used for lewisiteproduction, if the arsenic trichlcride is omi ted, chlorovinylmercuricchloride is formed as the main product and vinyl chloride as aby-product; and an inert organic solvent may be used in the process.Omission of the organic solvent leads to the formation of vinyl chlorideand acetaldehyde as principal products in having the chlorovinylmercuricchloride react with aqueous hydrogen chloride as the polar reactant togive varying amounts of these products, depending on the concentrationof the acid. In these syntheses, the promoter is able to increase therate of reaction as it does in the production of lewisite by speeding upthe absorption of the acetylene by the catalyst.

In a like manner, the promoter may be used with the catalyst in atwo-step process wherein first an unsaturated hydrocarbon is absorbed ata promoted rate by the catalyst, and selectively so if desired at asuitable temperature, after which the catalyst absorbed hydrocarbon maybe reacted with another compound.

Promoter action of the type described is also of considerable industrialimportance in the addition of alcohols, ethers, anhydrides, esters,organic acid halides, hypochlorites, amines and other polar or aniccompounds to alkenes, alkadienes and alkynes.

Although the meanings of such terms as polar, non-polar, electropositiveand electronegative are well established, a brief explanation is givenherewith for clarification. It is well recognized that elements andgroups of elements can be arranged in order starting with the mostelectropositive elements, the alkali metals, at one end and ending withthe most electronegative elements, e. g., fluorine, at the other end, asin the electromotive force series. The greater the separation betweenthe elements or groups on this scale, the greater is the ionic characterof the bond between such elements or groups. On this basis there islittle ionic character in C-C bonds, some in the 0-H bond, still more inC-0 and 0-01 bonds. Accordingly, the hydrocarbons are substantiallynon-polar, and many substituted organic compounds are relatively polar.A polar compound is a compound having ionic character. Also, from thedescribed scale each element or group has a certain relationship ofelectropositivity r electronegativity to the others. The trivalentarsenic ion in comparison to the divalent mercuric ion is moreelectrcpositive, but more electronegative compared to ions of zinc,iron, cadmium, tin and antimony. Arsenic is more electropositive thanphosphorus. Although arsenic trichloride is a polar compound, it is lesspolar than the described polar promoters since arsenic is closer inelectronegativity to chlorine than the metals of the promoterAccordingly, arsenic trichloride, even though inor ganic, tends toexhibit properties of polar organic compounds and has a highersolubility in organic solvents than the promoters. Likewise, thepreferred catalysts are less polar than the preferred promoters, thustending to be more soluble in organic solvents than the preferredpromoters.

On the basis or" the foregoing description, is to be noted that animproved synthesis of this invention involves a reaction of asubstantially nonpolar organic compound, such as an unsaturatedhydrocarbon, and a relatively polar organic or inorganic compound, suchas chlorovinyldichloroarsine or arsenic trichloride, with theintervention of a catalyst of low polarity, such as mercuric chloride,and a promoter of higher polarity, such as antimony trichloride.

While the relationship of polarity of the reactants, catalyst andpromoter is a main factor of the suitability of a substance as apromoter in the reaction, there are other factors to be considered, asalready explained. For instance, in an aqueous catalytic solution, thepromoter is preferably a substance which does not hydrolyze too much,does not precipitate out too much of the catalyst, and does not reactreadily with the non-polar reactant. While each of these factors alsohas a relationship to polarity, the selection of a particular promoterdepends upon the particular reactant, catalyst and conditions ofreaction.

It is to be understood that the invention is not limited by the specificexamples given for the purpose of illustration nor by any theory on themechanism of the promoter action and that various modifications comeWithin the spirit and scope of the invention.

We claim:

1. In the synthesis of chlorovinyldichloroarsine from acetylene andarsenic chloride, the steps comprising catalyzing the reaction with anaqueous hydrochloric acid solution of mercuric chloride, furtherincreasing the rate of reaction by adding to the solution antimonytrichloride to the extent that some of the antimony trichlcride becomesdissolved in the chlorovinyl dichloroarsine product, and recoveringdissolved antimony trichloride from said product by extraction withhydrochloric acid.

2. In the synthesis of chlorovinyl dichloroarsine from acetylene andarsenic chloride, the steps comprising catalyzing the reaction with anaqueous hydrochloric acid solution of mercuric chloride, furtherincreasing the rate of reaction by adding to the solution antimonytrichlcride to the extent that some of the antimony trichloride becomesdissolved in the chlorovinyl dichloroarsine product and recoveringdissolved antimony trichloride from said product by extraction withhydrochloric acid, said antimony chloride remaining mostly dissolved andunhydrolyzed in said solution.

3. I'he method of preparing chlorovinyl dichloroarsine which comprisesreacting a mixture of acetylene and arsenic trichloride at a suitablereaction temperature with an aqueous solution of a mercuric chloridecatalyst and a promoter selected from the group consisting of antimonytrichloride, antimony pentachloride, cadmium chloride, zinc chloride,stannic chloride, and ferric chloride which remains mostly dissolved andunhydrolyzed in said solution.

4. The method of claim 2, wherein the promoter is zinc chloride.

5. The method of claim 2, wherein the promoter is stannic chloride.

6. The method of claim 2, wherein the promoter is antimony trichloride.

PAUL D. BARTLETT. HYP JOSEPH DAUBEN, JR. LEONARD J. ROSEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date Great Britain 1913Great Britain 1925 OTHER REFERENCES Mann and Pope, Jour. Chem. Soc.(London), vol. 121 (1922).

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